Mutations in DNA Mutations Mutations changes in the

Mutations in DNA

Mutations • Mutations: changes in the DNA nucleotide sequence • Occurs when: – Errors are made during DNA replication (copying) – Errors are made during transcription – DNA is exposed to mutagens • Source of variation in living things

How do mutations affect the cell? • Fact 1: Sequence of DNA codes for the sequence of amino acids • Fact 2: Sequence of amino acids determines the shape of the protein • Fact 3: Shape of a protein determines the proteins functions (capabilities). • Question: What’s the problem with mutations? • Answer: Mutations can create nonfunctioning or malfunctioning proteins

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Is mutation a bad word? • Sometimes, yes! • Many times, no! – Mutations create variation in populations – Variations can give individuals a greater chance for survival (blubber in a whale, fighting off an infection because of a newly shaped immune system protein) – Some mutations are “silent” in that they do not affect protein shape and/or function

If I have a mutation in a gene thats important for survival, will I die? • Depends on severity of mutation (how badly it alters the protein) • Remember– we have TWO copies of each gene (one from mom, one from dad). – If one “normal copy” of a gene compensates for a “broken copy”, the mutation is called recessive – If one broken copy is enough to do damage, called a dominant mutation

Sickle Cell Point Mutation

Sickle vs. normal RBC

Phenylketonuria (PKU) • Caused by a recessive mutation in the gene that codes for an enzyme (PAH) that converts phenylalanine, an amino acid, to tyrosine, another amino acid • Build up of phenylalanine byproduct causes mental retardation • http: //www. dnaftb. org/ygyh/pku/cause. htm

Albinism • Caused by a recessive mutation in a gene that codes for an enzyme that makes melanin • Melanin gives hair, skin, and eyes pigmentation, so a lack causes paleness – Problems: sunburn, skin cancer, retina damage

Tay-Sachs • Recessive mutation in a gene that codes for a protein that prevents lipid build up in brain cells. – Lipid build up destroys brain cells • Death occurs in early childhood • More common in Ashkenazi Jewish populations

Cystic Fibrosis (CF) and Huntington Disease (HD) • CF: Recessive mutation that causes damage to the lungs and pancreas • HD: Dominant mutation that causes progressive breakdown of brain cells. – Occurs in middle age.